Inhibiting proliferation of cancer cells

ABSTRACT

A method of testing cancer cells is described. Assays are provided for determining the potential for inhibiting cancer cells proliferation using albumin-derived peptides. The methods of the present invention allow for drug screening as well as for evaluation of biopsied tumors.

FIELD OF THE INVENTION

[0001] The invention generally relates to the inhibition of cancer cell proliferation, and, more specifically, to the testing of cancer cells for their ability to be inhibited, and to the identification and use of drugs to inhibit cancer cell proliferation.

BACKGROUND

[0002] The term “chemotherapy” simply means the treatment of disease with chemical substances. The father of chemotherapy, Paul Ehrlich, imagined the perfect chemotherapeutic as a “magic bullet;” such a compound would kill invading organisms without harming the host. This target specificity is sought in all types of chemotherapeutics, including anticancer agents.

[0003] However, specificity has been the major problem with anticancer agents. In the case of anticancer agents, the drug needs to distinguish between host cells that are cancerous and host cells that are not cancerous. The vast bulk of anticancer drugs are indiscriminate at this level. Typically anticancer agents have negative hematological effects (e.g., cessation of mitosis and disintegration of formed elements in marrow and lymphoid tissues), and immunosuppressive action (e.g., depressed cell counts), as well as a severe impact on epithelial tissues (e.g., intestinal mucosa), reproductive tissues (e.g., impairment of spermatogenesis), and the nervous system. P. Calabresi and B.A. Chabner, In: Goodman and Gilman The Pharmacological Basis of Therapeutics (Pergamon Press, 8th Edition) (pp. 1209-1216).

[0004] What is needed is a specific anticancer approach that is particularly suitable for specific cancer cells. Importantly, the treatment must be effective with minimal host toxicity.

SUMMARY OF THE INVENTION

[0005] The invention generally relates to the inhibition of cancer cell proliferation, and, more specifically, to the testing of cancer cells for their ability to be inhibited, and to the identification and use of drugs to inhibit cancer cell proliferation. The present invention provides A) an in vitro model for testing cancer cells and evaluating their potential for being inhibited, B) a screening assay for identifying drugs that inhibit cancer cell proliferation, and C) chemotherapeutics for inhibiting cancer cell proliferation in vivo.

[0006] A variety of assay formats are contemplated for testing the potential for inhibiting cancer cells. In one embodiment, a portion of a patient's tumor is obtained (e.g., by biopsy) and placed in tissue culture. Thereafter, the response of the cancer cells to a albumin-derived peptide is assessed. Where the albumin-derived peptide inhibits proliferation, the tumor can be considered to be expressing the corresponding plasma membrane receptor and such a tumor may be suitable for chemotherapeutics that target this receptor. The potential for reversing or overcoming this inhibition with hormone (e.g. estradiol) can also be assessed by adding the hormone to the culture. Where the inhibition with the albumin-derived peptide is cancelled by the presence of the hormone, the tumor can be considered to be expressing the corresponding plasma membrane hormone-binding receptor and such a tumor may be suitable for chemotherapeutics that target this particular receptor. Moreover, other therapies may be adopted that those skilled in the art recognize to be appropriate for “hormone sensitive” tumors.

[0007] In one embodiment, the present invention contemplates a method of evaluating human cancer comprising: a) providing i) a human cancer patient, and ii) an albumin-derived peptide; b) obtaining cancer cells from said patient; c) contacting said cells ex vivo with said albumin-derived peptide; and d) measuring cancer cell proliferation. Preferably the cancer cells are cultured in serun-free culture media so as to essentially avoid introducing complicating factors. In another embodiment, the present invention provides a method of testing human cancer cells comprising: a) providing i) a human cancer patient, ii) an albumin-derived peptide, and iii) one or more hormones or hormone analogues; b) obtaining cancer cells from said patient; c) culturing said cells in serum-free culture media in the presence of said albumin-derived peptide and said one or more hormones or hormone analogues; and d) measuring cancer cell proliferation.

[0008] As noted above, the present invention also contemplates a screening assay for identifying drugs that inhibit tumor invasion. The present invention contemplates a screening assay utilizing the binding activity of albumin-derived peptides. In one embodiment, cancer cells (whether obtained from a primary tumor or grown as an established cell line) are placed in tissue culture in the presence of an albumin-derived peptide. It is contemplated that an inhibitable tumor cells cultured in the presence of the albumin-derived peptide will not proliferate. In the drug screening assay, candidate drug inhibitors are added to a second tissue culture containing the inhibitable tumor cells (this can be done individually or in mixtures). Where the inhibitable cells are found to be similarly inhibited by the candidate drug, a drug inhibitor is indicated (hereinafter a “type 1 drug inhibitor”). It is also contemplated that the drug screening be done in the presence of a blocking hormone, i.e. a hormone that overcomes or cancels the inhibition caused by the albumin-derived peptide. For example, where the inhibition by the albumin-derived peptide is cancelled by the addition of estradiol, a candidate drug can be added in an attempt to interfere with the action of the hormone. Where the presence of estradiol does not result in proliferation, a second type of drug inhibitor is indicated (hereinafter a “type 2 drug inhibitor”). It is not intended that the present invention be limited by the nature of the drugs screened in the screening assay of the present invention. A variety of drugs, including peptides, are contemplated. Antibodies to albumin, the hormone or the corresponding receptors are contemplated as convenient positive controls.

[0009] In one embodiment, the present invention contemplates a method of screening drugs comprising: a) providing: i) albumin-inhibitable tumor cells, ii)an inhibitor selected from the group consisting of albumin, an albumin-derived peptide, and an albumin-derived peptide analogue, iii) one or more steroid hormones, and iv) a candidate drug; b) contacting said cells in vitro with said inhibitor, said one or more steroid hormones and said candidate drug; and c) measuring the extent of tumor cell proliferation.

[0010] It is not intended that the present invention be limited by the means by which the extent of proliferation is measured. A variety of quantitative and qualitative means is known in the art, including (but not limited to): 1) the uptake of radiolabelled nucleic acid precursors (e.g. tritiated thymidine), 2) microscopic examination, and 3) automated cell counting (including lysing cells and counting nuclei).

[0011] It is not intended that the present invention be limited by the nature of the cancer cells used for drug screening. Both i) cancer cells from established cancer cell lines and ii) cancer cells obtained from patients (e.g. from a biopsy) are contemplated. A variety of tumor types are contemplated as well, including, but not limited to, breast cancer cells and prostate cancer cells.

[0012] Finally, the present invention contemplates chemotherapeutics for treating cancer in vivo. In one embodiment, the present invention contemplates chemotherapeutics to inhibit cancer cell proliferation. Both type 1 and type 2 drug inhibitors identified through the above-described screening assay are contemplated. Moreover, albumin-derived peptides and peptide analogues are specifically contemplated for in vivo use. In one embodiment, the method comprises administering an albumin-derived peptide or peptide analogue as adjunct therapy with additional chemotherapeutics.

DESCRIPTION OF THE FIGURES

[0013]FIG. 1 shows an amino acid sequence representative of human serum albumin.

[0014]FIG. 2 depicts the DNA sequence coding for mature HSA.

[0015]FIG. 3 shows the SDS-PAGE results for albumin and albumin-derived peptides.

[0016]FIG. 4 is a graph showing the dose response of cancer cells to albumin in the presence and absence of estradiol.

DEFINITIONS

[0017] The term “drug” as used herein, refers to any medicinal substance used in humans or other animals. Encompassed within this definition are naturally occurring and synthetic organic compounds, as well as naturally occurring and synthetic recombinant pharmaceuticals (whether hormones, peptides or peptide analogues).

[0018] The term “hormone” refers to trace substances produced by various endocrine glands which serve as chemical messengers carried by the blood to various target organs, where they regulate a variety of physiological and metabolic activities in vertebrates. The steroid hormones include the estrogens, or female sex hormones, the androgens, or male hormones (testosterone, dihydrotestosterone); the progestational hormone progesterone; and the steroid hormones of the adrenal cortex (major forms, cortisol, aldosterone, and corticosterone).

[0019] The term “albumin-derived peptide” refers to a peptide having a sequence that is identical to a portion of the amino acid sequence of albumin. The present invention also contemplates analogues. In one embodiment, an “albumin-derived peptide analogue” comprises a peptide having a sequence that is similar (but not identical) to a portion of the amino acid sequence of albumin. In another embodiment, an “albumin-derived peptide analogue” is a “mimetic.” Mimetics are compounds mimicking the necessary conformation for recognition and docking to the receptor binding to the albumin-derived peptide.

[0020] The term “receptors” refers to structures expressed by cells and which recognize binding molecules (e.g. ligands).

[0021] The term “antagonist” refers to molecules or compounds which inhibit the action of a “native” or “natural” compound (such as albumin). Antagonists may or may not be homologous to these natural compounds in respect to conformation, charge or other characteristics. Thus, antagonists may be recognized by the same or different receptors that are recognized by the natural compound.

[0022] The term “host cell” refers to any cell which is used in any of the screening assays of the present invention. “Host cell” also refers to any cell which either naturally expresses particular receptors of interest or is genetically altered so as to produce these normal or mutated receptors.

DESCRIPTION OF THE INVENTION

[0023] As noted above, chemotherapeutic agents are currently employed to reduce the unrestricted growth of cancer cells. However, better agents are needed that more specific and less toxic. The invention generally relates to the inhibition of cancer cell proliferation, and, more specifically, to the testing of cancer cells for their ability to be inhibited, and to the identification and use of drugs to inhibit cancer cell proliferation.

[0024] A. Assays For Inhibiting Cancer Cell Proliferation

[0025] Discovering how to inhibit the proliferation of tumor cells first requires the development of assays with which to test the potential for tumor cells to be inhibited. The present invention contemplates a variety of in vitro assays involving the use of albumin and/or albumin-derived peptides.

[0026] Albumin and Making Albumin-Derived Peptides

[0027] In one assay system, the present invention contemplates using albumin and/or albumin-derived peptides. Human serum albumin (HSA) is the most abundant plasma protein. A molecule of HSA consists of a single non-glycosylated polypeptide chain of 585 amino acids of formula molecular weight 66,500. A representative amino acid sequence of HSA is shown in FIG. 1. Variations in the sequence are known. As used herein, “variants of human serum albumin” are those sequence showing greater than 80% homology, and preferably greater than 90% homology, and most preferably greater than 95% homology, to the sequence set forth in FIG. 1.

[0028] Albumin-derived peptides are those peptides having a sequence that is identical to a portion of the amino acid sequence of albumin as set forth in FIG. 1. In one embodiment, the present invention contemplates an albumin-derived peptide comprising the N-terminal portion of human serum albumin up to amino acid residue n, where n is between 360 and 430, are more preferably between 369 and 419.

[0029] In one embodiment, an “albumin-derived peptide analogue” comprises a peptide having a sequence that is similar (but not identical) to a portion of the amino acid sequence of albumin as set forth in FIG. 1. Such similar sequences are contemplated to have conservative substitutions and/or deletions and/or additions.

[0030] Conservative substitutions are those where one or more amino acids are substituted for others having similar properties in the understanding of one skilled in the art. Typical substitutions include, but are not limited by, substitutions of alanine or valine for glycine, arginine or asparagine for glutamine, serine for threonine and histidine for lysine.

[0031] Analogues having deletions are those having up to ten (and preferably only one or two) amino acid residues lacking (in comparison to the sequence set forth in FIG. 1). Preferably, such deletions occur in the portion between 1 and 370, and more preferably between 100 and 369.

[0032] Analogues having additions are those peptides that encompass additional amino acid residues, including whole sequences which are not native to HSA. In one embodiment, the peptide analogue having additions comprises a peptide between one hundred and five hundred amino acids in length. In one embodiment, the peptide analogue having additions comprises additional amino acids added to the amino terminus of an albumin-derived sequence. In one embodiment, the peptide analogue having additions comprises additional amino acids added to the carboxy terminus of an albumin-derived sequence. In another embodiment, the peptide analogue having additions comprises additional amino acids added to both the amino and carboxy termini.

[0033] One common methodology for evaluating sequence homology, and more importantly statistically significant similarities, is to use a Monte Carlo analysis using an algorithm written by Lipman and Pearson to obtain a Z value. According to this analysis, a Z value greater than 6 indicates probable significance, and a Z value greater than 10 is considered to be statistically significant. W. R. Pearson and D. J. Lipman, Proc. Natl. Acad. Sci. (USA), 85:2444-2448 (1988); D. J. Lipman and W. R. Pearson, Science, 227:1435-1441 (1985). In the present invention, synthetic albumin-derived peptide analogues are those peptides with statistically significant sequence homology and similarity (Z value of Lipman and Pearson algorithm in Monte Carlo analysis exceeding 6).

[0034] Preferred albumin-derived peptides include, but are limited to, HSA (1-373) (i.e. where the C-terminal amino acid is Val); HSA (1-387) (i.e. where the C-terminal amino acid is Leu); HSA (1-388) (i.e. where the C-terminal amino acid is I1e); HSA (1-379) (i.e. where the C-terminal amino acid is Lys); HSA (1-390) (i.e. where the C-terminal amino acid is Gln); and HSA (1-407) (i.e. where the C-terminal amino acid is Leu).

[0035] It is not intended that the present invention be limited by the manner in which the albumin-derived peptide is made. In one embodiment, the peptide is made by enzymatic digestion. For example, a trypsin-like enzyme will cleave HSA between Lys (389) and Gln (390), as well as at other sites. In another embodiment, the peptide is made by peptide synthesis. In still another embodiment, Albumin-derived peptides are conveniently made by recombinant techniques. See U.S. Pat. No. 5,380,712, hereby incorporated by reference. FIG. 2 depicts the DNA sequence coding for mature HSA. This sequence can be used together with standard recombinant DNA procedures to construct expression vectors for the expression of albumin-derived peptides.

[0036] It is not intended that the present invention be limited by the precise amount of albumin or albumin-derived peptide used in the assays of the present invention. When albumin is used, the inhibiting concentration of albumin is typically between one microgram and two milligram per milliliter of culture fluid, and more preferably greater than one hundred micrograms per milliliter and less than one milligram per milliliter.

[0037] B. Drug Screening Assays

[0038] As noted above, the present invention also contemplates a screening assay for identifying drugs that inhibit cancer cell proliferation. The present invention contemplates a screening assay utilizing the binding activity of albumin and/or albumin-derived peptides, including but not limited to the above-described peptides. In one embodiment, an inhibitable tumor cell line is placed in tissue culture. The tumor cells (under ordinary conditions) will proliferate; however, in the presence of albumin and/or albumin-derived peptides, the cell proliferation will be inhibited.

[0039] In the drug screening assay of the present invention, candidate drug inhibitors are added to the tissue culture (this can be done individually or in mixtures). Where the cancer cells are found to be inhibited, a drug inhibitor is indicated.

[0040] It is not intended that the present invention be limited by the nature of the drugs screened in the screening assay of the present invention. A variety of drugs, including peptides, are contemplated.

[0041] It is also not intended that the present invention be limited by the particular tumor cells used for drug testing. A variety of tumor cells (for both positive and negative controls) are contemplated (including but not limited to the cells set forth in Table 1 below). In addition, primary tumor cells from patients are contemplated.

[0042] Where the inhibitable cells are found to be similarly inhibited by the candidate drug, a drug inhibitor is indicated (hereinafter a “type 1 drug inhibitor”). It is also contemplated that the drug screening be done in the presence of a blocking hormone, Lie. a hormone that overcomes or cancels the inhibition caused by the albumin-derived peptide. Where the presence of a hormone does not result in proliferation, a second type of drug inhibitor is indicated (hereinafter a “type 2 drug inhibitor”). It is not intended that the present invention be limited by the nature of the hormone used in conjunction with the drug screening assay. As discussed below, the present invention contemplates hormones mediating cell proliferation.

[0043] Hormones Mediating Proliferation of Cancer Cells

[0044] While an understanding of the mechanisms involved in cancer is not necessary to the successful practice of the present invention, it is believed that hormones can mediate the proliferation of cancer cells. The present invention contemplates the use of steroid sex hormones in conjunction with the assays for testing cancer cells. TABLE 1 Designation And Origin Of Human Cell Lines And Strains¹ ORIGIN CELL LINES OR STRAINS Colonic carcinoma SW1116, HCT116, SKCO-1, HT-29, KM12C, KM12SM, KM12L4, SW480 Pancreatic carcinoma BxPC-3, AsPC-1, Capan-2, MIA PaCa-2, Hs766T Colon adenoma VaCo 235 Lung carcinoma A549 Prostate carcinoma PC-3, DU-145 Breast cancer 009P, 013T, MCF-7, MDA-MB231 Lymphoma Daudi, Raji Breast epithelium 006FA Diploid fibroblast HCS (human corneal stroma), MRC-5

[0045] Naturally occurring or endogenous estrogens constitute one class of steroid sex hormones which are produced in the ovaries and other tissues in the body. The naturally occurring estrogens are estrone (also known as E₁), estradiol-17B (also known as E₂), and estriol (also known as E₃). Synthetic compounds having estrogenic properties include ethinyl estradiol (Estinyl); 3-methyl-ethinyl estradiol (Mestranol); and diethylstilbestrol (DES); methallenestril (Vallestril); and doisynoestrol (Fenocylin).

[0046] The present invention contemplates testing the response of the cancer cells to albumin and albumin-derived peptides. Where the albumin-derived peptide inhibits proliferation, the tumor can be considered to be expressing the corresponding plasma membrane receptor and such a tumor may be suitable for chemotherapeutics that target this receptor. The potential for reversing or overcoming this inhibition with hormone (e.g. estradiol) can also be assessed by adding the hormone to the culture. Where the inhibition with the albumin-derived peptide is cancelled by the presence of the hormone, the tumor can be considered to be expressing the corresponding plasma membrane hormone-binding receptor and such a tumor may be suitable for chemotherapeutics that target this particular receptor. Moreover, other therapies may be adopted that those skilled in the art recognize to be appropriate for “hormone sensitive” tumors.

[0047] A variety of formats and protocols for testing hormones is contemplated. Illustrative formats and protocols are described in U.S. Pat. Nos. 4,859,585 and 5,135,849, both of which are hereby incorporated by reference.

[0048] C. Administering Chemotherapeutics

[0049] It is contemplated that albumin, albumin-derived peptides, and albumin-derived peptide analogues, as well as the type 1 and type 2 drugs discussed above, can be administered systemically or locally to inhibit tumor cell proliferation in cancer patients. They can be administered intravenously, intrathecally, intraperitoneally as well as orally. Moreover, they can be administered alone or in combination with anti-proliferative drugs.

[0050] Where combinations are contemplated, it is not intended that the present invention be limited by the particular nature of the combination. The present invention contemplates combinations as simple mixtures as well as chemical hybrids. An example of the latter is where the peptide or drug is covalently linked to a targeting carrier or to an active pharmaceutical. Covalent binding can be accomplished by any one of many commercially available crosslinking compounds.

[0051] It is not intended that the present invention be limited by the particular nature of the therapeutic preparation. For example, such compositions can be provided together with physiologically tolerable liquid, gel or solid carriers, diluents, adjuvants and excipients.

[0052] These therapeutic preparations can be administered to mammals for veterinary use, such as with domestic animals, and clinical use in humans in a manner similar to other therapeutic agents. In general, the dosage required for therapeutic efficacy will vary according to the type of use and mode of administration, as well as the particularized requirements of individual hosts.

[0053] Such compositions are typically prepared as liquid solutions or suspensions, or in solid forms. Oral formulations for cancer usually will include such normally employed additives such as binders, fillers, carriers, preservatives, stabilizing agents, emulsifiers, buffers and excipients as, for example, pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, sodium saccharin, cellulose, magnesium carbonate, and the like. These compositions take the form of solutions, suspensions, tablets, pills, capsules, sustained release formulations, or powders, and typically contain 1%-95% of active ingredient, preferably 2%-70%.

[0054] The compositions are also prepared as injectables, either as liquid solutions or suspensions; solid forms suitable for solution in, or suspension in, liquid prior to injection may also be prepared.

[0055] The antagonists of the present invention are often mixed with diluents or excipients which are physiological tolerable and compatible. Suitable diluents and excipients are, for example, water, saline, dextrose, glycerol, or the like, and combinations thereof. In addition, if desired the compositions may contain minor amounts of auxiliary substances such as wetting or emulsifying agents, stabilizing or pH buffering agents.

[0056] Additional formulations which are suitable for other modes of administration, such as topical administration, include salves, tinctures, creams, lotions, and, in some cases, suppositories. For salves and creams, traditional binders, carriers and excipients may include, for example, polyalkylene glycols or triglycerides.

[0057] Designing Mimetics

[0058] It may be desirable to administer an analogue of an albumin-derived peptide. As mentioned previously, the present invention contemplates compounds mimicking the necessary conformation for recognition and docking to the albumin receptor. A variety of designs for such mimetics are possible. For example, cyclic peptides, in which the necessary conformation for binding is stabilized by nonpeptides, are specifically contemplated. U.S. Pat. No. 5,192,746 to Lobl et al., U.S. Pat. No. 5,169,862 to Burke, Jr. et al., U.S. Patent No. 5,539,085 to Bischoff et al., U.S. Patent No. 5,576,423 to Aversa et al., U.S. Pat. No. 5,051,448 to Shashoua, and U.S. Patent No. 5,559,103 to Gaeta et al., all hereby incorporated by reference, describe multiple methods for creating such compounds.

[0059] Synthesis of nonpeptide compounds that mimic peptide sequences is also known in the art. Eldred et al., (J. Med. Chem. 37:3882 (1994)) describe nonpeptide antagonists that mimic the Arg-Gly-Asp sequence. Likewise, Ku et al., (J. Med. Chem. 38:9 (1995)) give further elucidation of the synthesis of a series of such compounds. Such nonpeptide compounds are specifically contemplated by the present invention.

[0060] The present invention also contemplates synthetic mimicking compounds that are multimeric compounds that repeat the relevant peptide sequence. As is known in the art, peptides can be synthesized by linking an amino group to a carboxyl group that has been activated by reaction with a coupling agent, such as dicyclohexyl-carbodiimide (DCC). The attack of a free amino group on the activated carboxyl leads to the formation of a peptide bond and the release of dicyclohexylurea. It can be necessary to protect potentially reactive groups other than the amino and carboxyl groups intended to react. For example, the (x-amino group of the component containing the activated carboxyl group can be blocked with a tertbutyloxycarbonyl group. This protecting group can be subsequently removed by exposing the peptide to dilute acid, which leaves peptide bonds intact.

[0061] With this method, peptides can be readily synthesized by a solid phase method by adding amino acids stepwise to a growing peptide chain that is linked to an insoluble matrix, such as polystyrene beads. The carboxyl-terminal amino acid (with an amino protecting group) of the desired peptide sequence is first anchored to the polystyrene beads. The protecting group of the amino acid is then removed. The next amino acid (with the protecting group) is added with the coupling agent. This is followed by a washing cycle. The cycle is repeated as necessary.

[0062] Experimental

[0063] The following examples serve to illustrate certain preferred embodiments and aspects of the present invention and are not to be construed as limiting the scope thereof.

[0064] In the experimental disclosure which follows, the following abbreviations apply: eq (equivalents); M (Molar); μM (micromolar); mM (millimolar); N (Normal); mol (moles); mmol (millimoles); μmol (micromoles); nmol (nanomoles); g (grams); mg (milligrams); μg (micrograms); L (liters); ml (milliliters); μl (microliters); cm (centimeters); mm (millimeters); μm (micrometers); nm (nanometers);° C. (degrees Centigrade); mAb (monoclonal antibody); MW (molecular weight); PBS (phosphate buffered saline); U (units); d(days).

[0065] A clonal population of the human breast cancer MCF-7 cell line was used in some of the experiments described below. These cells were routinely grown in 5% fetal bovine serum (FBS) supplemented-Dulbecco's Modified Eagle's Medium (DME). Charcoal-dextran (CD) stripped serum-supplemented medium inhibits their proliferation and estradiol cancels this effect. Estrogen non-target, serum-insensitive human breast cancer MDA-MB231 cells (ATCC, Rockville, Md.) were used as controls; they were grown under the same conditions as MCF-7 cells.

[0066] Recombinant human albumin (rHA), recombinant Domain I (aa 1-194, rDI) and Domain I+II (aa 1-387, rDI+II) were obtained from Delta Biotechnology Ltd., Nottingham, U. K. rHA and truncated HA transcripts were produced in yeast grown in synthetic medium comprising sucrose, vitamins and inorganic salts.

[0067] At chosen intervals after exposure to 2 mg/ml rHA with or without 100 pM estradiol, cells were trypsinized, pelleted by centrifugation at 100 g for 3 min, resuspended in 10% DMSO-10% CDHuS and snap frozen. Cells were kept at −20° C. for up to 7 days. Cells were quickly thawed at 37° C., centrifuged and resuspended at a density of 10⁶ cells/ml in a solution containing 0.1% Triton X-100, 0.1 mg/ml propidium iodide (PI) (Sigma) in DME. Total DNA was quantified by propidium iodide binding. The RNAse treatment used in the original method to hydrolyze double stranded RNA did not significantly affect the DNA fluorescence and was omitted. Cells were analyzed in a Becton-Dickinson FACSCAN flow cytometer. Ten thousand cells were collected for each point. Data were collected and compiled with Becton-Dickinson Lysis II and Cell Fit software.

[0068] HA-free serum was obtained by Cibracron Blue and by hexyl-S agarose chromatography. Ten millilitres of CD stripped serum were dialyzed against start buffer [500 mM NaCl, 500 mM K₂SO₄, 50 mM sodium phosphate buffer (SPB) pH 7.6 containing 10 uM butylated hydroxytoluene (BHT)] and chromatographed through a 1.6×12 cm hexyl-S agarose column. After extensive elution of the breakthrough proteins, the retained fraction (HA) was eluted first with 5 mM SPB, pH 7.6, containing 10 uM BHT, and finally with 40% ethylene glycol in 50 mM SPB, pH 7.6, containing 10 uM BHT. Removal of HA was monitored electrophoretically and by immunoblots. The three hexyl-S agarose fractions were dialyzed against a buffer suitable for tissue culture (100 mM NaCl, 25 mM Hepes, pH 7.4, containing 1 uM BHT) and their effect on cell proliferation tested at concentrations ranging from 0.25 to mg/ml of protein in ITDME.

[0069] In some experiments, serum and recombinant proteins were analyses by ID-sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE) using 12.5% homogeneous and 10-15% gradient polyacrylamide gels and SDS buffer strips in the electrophoresis Phast System (Pharmacia, Piscataway, N.J.). Gels were stained with Coomassie blue. Gel images were digitized and analyses using the BioImage, whole band software package (Millipore Corp., Bedford, Mass.).

[0070] A polyclonal antibody was obtained in rabbits using as antigen serum albumin (Sigma; cat. no. A1887); it was purified by chromatography through tandem columns of butyl-S and hexyl-S agarose as described by Porath. The immunoglobulin fraction was precipitated with 2.2 M (NH₄)₂SO₄, dialyzed and purified by affinity chromatography using as immunoadsorbant rHA coupled to CNBr-activated Sepharose-4B. A monoclonal mouse anti-HA IgG (Sigma; cat. no. A6684) and a polyclonal anti-HA serum (cat. no. 126582, lot 703293) supplied by Calbiochem (Richmond, Calif.) gave similar results. However, the monoclonal antibody was the most sensitive one; as little as 0.5 mg HA/lane were clearly resolved as a band by the Biolmage software. Serum proteins were resolved by SDS-PAGE, transferred electrophoretically onto Immobilon-P membranes using the Phast System (ID-PAGE). Membranes were blocked with 60 mg/l teleostean gelatin, reacted with the monoclonal antibody (1:20000), rinsed, and processed with a VEctastain ABC-Ap kit (Vector, Inc., Burlingame, Calif.) for reaction with the second antibody and alkaline phosphatase following the protocol, described by the manufacturer. Immunoreactive bands were visualized after incubation with the substrate [5-bromo-1-chloro-3-indolyl phosphate/nitroblue tetrazolium BCIP/NBT substrate kit (Vector)].

EXAMPLE 1 Inhibitory Effects of Albumin

[0071] To assess the inhibitory effect of serum or purified protein preparations, 4×10⁴ cells/well were seeded in 12-well Falcon Multiplates in 5% FBS; they were allowed to attach for 24 h before exposing them to test medium. Cell proliferation yields were measured after 4 days in DME plus 25 ug transferrin (T)/ml and 100 ng insulin (I)/ml (TTDME) alone, or ITDME plus CD human serum (CDHuS), or purified protein preparations. Each sample was tested in duplicate in the presence or absence of 100 pM estradiol (E₂) and each experiment was repeated at least three times. Phenol red-free media were used in all experiments involving cell proliferation rates or yields. Cells were lysed and nuclei counted on a Coulter Counter Model ZM. Estrogens were removed from serum, HA (Sigma Chemical Co.; cat. no. A1887) and from rHA preparations by CD stripping.

[0072] As seen in FIG. 4, CDHuS (open diamonds) and CDHA (open circles) inhibited the proliferation of MCF-7 cells in a dose-dependent manner; similarly, rHA (closed diamonds) inhibited the proliferation of these cells. Estradiol (closed squares) reversed the inhibitory effect. Progesterone, 5α-dihydrotestosterone, the synthetic androgen R1881, hydrocortisone, and thyroxine failed to reverse the effect of rHA (data not shown).

EXAMPLE 2 Inhibitory Activity of Truncated Forms of rHA

[0073] To assess whether the inhibitory activity of albumin was encoded in a specific sequence within the albumin molecule, the inhibitory effect of truncated peptides encoding the first domain alone and the first and second domains (see FIG. 3) was tested in the manner that rHA was tested in Example 1.

[0074] The inhibitory activity of dDI+II was comparable to that of rHA; rDI also showed inhibitory activity, albeit quantitatively lower than that of rHA or rDI+II, both when expressed as a molar concentration and as mg/ml (data not shown).

EXAMPLE 3 Conjugation of Albumin-derived Peptides

[0075] In this example, the preparation of a peptide conjugate is described. As noted above, the albumin-derived peptides of the present invention can be made synthetically or recombinantly. A cysteine can be added to facilitate conjugation to other proteins.

[0076] In order to prepare a protein for conjugation, it is dissolved in buffer (e.g., 0.01 M NaPO₄, pH 7.0) to a final concentration of approximately 20 mg/ml. At the same time n-maleimidobenzoyl-N-hydroxysuccinimide ester (“MBS” available from Pierce) is dissolved in N,N-dimethyl formamide to a concentration of 5 mg/ml. The MBS solution, 0.51 ml, is added to 3.25 ml of the protein solution and incubated for 30 minutes at room temperature with stirring every 5 minutes. The MBS-activated protein is then purified by chromatography on a Bio-Gel P-10 column (Bio-Rad; 40 ml bed volume) equilibrated with 50 mM NaPO₄, pH 7.0 buffer. Peak fractions are pooled (6.0 ml).

[0077] The above-described cysteine-modified peptide (20 mg) is added to the activated protein mixture, stirred until the peptide is dissolved and incubated 3 hours at room temperature. Within 20 minutes, the reaction mixture becomes cloudy and precipitates form. After 3 hours, the reaction mixture is centrifuged at- 10,000×g for 10 min and the supernatant analyzed for protein content. The conjugate precipitate is washed three times with PBS and stored at 4° C.

[0078] From the above, it should be clear that the present invention provides a method of testing of cancer cells,and in particular identifying cancer cells that are inhibitable as well as hormone sensitive. With regard to the later, distinguishing such tumors allows the physician to change and/or optimize therapy. Importantly, the albumin-derived peptides of the present invention (and other drugs developed by use of the screening assay of the present invention) will provide treatment associated with minimal host toxicity. 

1. A method of testing human cancer cells, comprising: a) providing: i) a human cancer patient, ii) an antibody to the receptor for human albumin; b) obtaining cancer cells from said patient; and c) contacting said cells ex vivo with said antibody.
 2. The method of claim 1, wherein said cancer cells are obtained from a biopsy.
 3. The method of claim 1, wherein said cancer cells are selected from the group consisting of breast cancer cells and prostate cancer cells.
 4. The method of claim 1, further comprising after step (b) and prior to step (c) the step of culturing said cancer cells.
 5. The method of claim 4, wherein said culturing is performed in serum-free media.
 6. The method of claim 1, further comprising after step (c) the step of detecting said antibody bound to said cells.
 7. A method of testing human cancer cells, comprising: a) providing: i) human cancer cells obtained from a biopsy; ii) an antibody specific for the human albumin receptor; and b) contacting said cells ex vivo with said antibody.
 8. The method of claim 7, wherein said cancer cells are selected from the group consisting of breast cancer cells and prostate cancer cells.
 9. The method of claim 7, further comprising prior to step (b) the step of culturing said cancer cells.
 10. The method of claim 9, wherein said culturing is performed in serum-free media.
 11. The method of claim 7, further comprising after step (b) the step of detecting said antibody bound to said cells. 